Rebalance bridge



Oct. 3, 1961 A. A. THIELE 3,003,108

assumes BRIDGE Filed Sept. 16, 195'! 2 Sheets-Shoot 1 Q A n urn c I a 1/ 8 I I 13 M Au WTWT pi. own a 1: sunu United States Patent 015cc sgoosnes REBALANCE BRIDGE AllredAJIhiele, 2502,15 om n-la man. FfledSept. 16, 1951, Ser. No. sugar 6Clalms. c1. sat-14o provide a current which simulates an input.

portional to the sum of theamplitndesof the two" signals.

Other objects of this invention are to provide a re-,

balance bridge and total amplitude sensing device which has a minimum size, minimum. of components, low heat dissipation, gain, temperature drift cancellation, and good s frequency response.

Another object of this invention is to provide a which can be used as a rebalance measuring device a failure indication device.

Another object of my invention is to provide a true with proportional control system which responds to a variable frequency signal and at thesame time receives amplitude and/or pulse modulation of thevariable frequency signal.

Other and further objects ofthis invention will become apparent in the following description and accompanying drawings wherein: FIG. 1' is a diagram of' the rebalance circuit. When later reference is made to the rebalance bridge it refers to the part. of the circuit included by points L M N X tand Y FIG. 2 is an equivalent transistor made of two transistors. FIG. 3 is the same as FIG. 1 except that the compound transistor of FIGURE 2 has been substituted: for the; singletransistors. is a. power control circuit for translating the output of the rebalance bridge into motor shaft rotationsv S is another t of the device shown in FIG. 4. FIG. 6' shows a. device for detecting an absence ot' signad to the rebalancebridge and. detecting audio signals. FIG. 7 shows a sample input device.

In FIG. 1: L M and N aretheinpm terminals. Bloclc lrrcpresents an input l Block 22 representa the FIG.4

otherinputl .TheseinputsmustbeD..ofitheeonect polarity for the inputs oil-he transistors, 3 and 4-. One of these transistors is the PNP type and the other I the NPN type. The circuit. is symmetrical and the orienta- .tion of the transistors is determined by the: polarity of the Voltage at points X and Y Aninput to either or: both of the transistors lowers the eflect'rve D.C-. resistance-of the transistor or transistors,- respeetively. If the ratio of the etfective. resistance of thetransistors is not the same as the ratio of the resistance of the sections on opposite sides of the variable tap of the resistor S appears a. voltage across points A and B The A' voltage in the other direction causes a movement in v the other direction. The circuit as so far. described would cause the output to. follow the input if it were not for the high A.C. collector resistance of thetransistors. This causes the effective D.C. resistance to lower with a decrease in voltage. This lowering of efiective resist- I ance with a decrease in voltage causes instability. This is overcome by the cross degeneration resistors 6 and 7. two resistors permit cach'transintotto ,depsnente'the Withthm degeneration'a change in collector voltage causes a L and the transistors act as base controlled variable rosistors. With the addition of these resistors the output device nowfollows the ratio of the input The addition of resistors G and 9 causes the output device to return to a point which is the inverse of their ratio in the absence of-an input. This is because the resistors 10 is fie power" supply for this circuit.

An example ofsuitable operating values for the of FIG; 1 is as follows 2 Transistors:

Resistors; I

8 meg" 1.5

9 meg" 1.5

1 FIG. 2 ,shows a transistor equivalent which may he substitutedfor the transistors in the rebalance circuit. This particular circuit consists of two common emitter connected transistors 12 and 13' which are direct coupled. If one of these transistors is of the NPN type the other must be ofthe PNP type. The equivalent base B'equivau lent collector C, and equivalent emitter E to a single transistor are indicated. Other equivalent transistors are found in Patent No. 2',663,806 by S. Darlington.

FIG. 3- is the same as FIG. 1 except the equivalent transistor of FIG. 2- is' substituted for the transistors The numbers are the same except for the subletter a.

operation is the same.

FlG; 4 is an output device'for converting the outpu at points A andB' into shaftrotations. 14 and 15 are transistors. 16 and 17 are. diodes. 18 and 19 are motor control relays. 20 is aD.C. motor. 21 is the motor power supply. 22 is the relay power supply.v The trans si's'tors are of the same type. When a voltage is: placed across points A and 8;, the points A; and B corresponding to the output points A; and B respectively, of FIG. 1, the voltageon the input of one transistor is of the wrong polarity to conduct. It is bypassed by a diode. The current then flows from the diode through the. input of the other transistor. Thus according to the polarity of the voltage across points A; and B one or the other of the transistors conducts. The correspondirlg relay then closes and the motor turns until the bridge is rebalanced; There is a mechanical connection from the output to therresistor 5, as shown by the phantom linkage displayed inFIG. l. I

FIG. 5 is an alternate device for converting the voltage at points A and B into shaft rotations. In this figure, 23 and 7A are transistors of the opposite polarities. 25 and 26 are motor control relays which are controlled by the transistors. 27 and 28 are the power supp-lies for each transistor. 29 is the rnotor and 30 is the motor power supply. The points A and B as shown in FIG. 1, are hereinafter referred to as A and B respectively. When a voltage is placed across points A and B it will cause one transistor to conduct but not the other according to the polarity of the transistor and voltage. This is because transistors of, opposite polarities such as NPN and P-NP require input voltages of opposite respective polarity to render them conductive. This closes the correspondingrelay, turns the motor and rebalances the bridge. q

The output device at points A and B may be any other type ofditferential relay or magnetic amplifier operating electrical, hydraulic, or pneumatic devices.

In FIG. 6 is. given the part of the circuit which detects input failuresand amplitude modulation ofv the Patented Oct. 3, 1961 formers are rectified in diodes 43, 44, 45 and 46.

signals. 31 is the power supply. 32 is the circuit of FIG. 1 or FIG. 3. Resistors 33 and 34 form a voltage divider which presents a constant voltage to the base of transistor 35 with reference to the power supply. In the rebalance section the resistor draws a nearly constant current. The transistors 3 and 4 draw a current which is proportion-a1 to the strength of the input signals from the sources 1 and 1 The resistor 36 conducts the sum of these two currents. The value of 36 and the voltage at the base of tranisstor 35 are chosen so that when an input signal is being received the emitter of the transistor 35 receives a D.C. signal of the wrong polarity and is cut oif. If, however, the signal is removed the current through 36 drops. The voltage across 36 drops and the emitter of the transistor 35 receives a DC. signal in the forward direction and it conducts'throwing relay 37. Thus by interrupting the input signal pulses may be sent to relay 37. If the input signal is amplitude modulated the audio signal may be picked up at point Z through capacitor 38. This signal results from the current variation through 36.

f An example of suitable operating values for parameters of FIG. 6 is as follows:

Transistor 35". CK721 the circuit Resistors:

33 40K 34---" K 36 0.5K Capacitor 38. .,u.f 0.1 Relay 37 5K FIG. 7 is a diagram of a discrirninator'inp-ut to points L7, M and N of the rebalance circuit. The points L M7 and N shown in FIG. 7 correspond to the input terminals L M and N respectively, as shown in FIG. 1. This is given so that typical remote control operation can be described. 39 is an input transistor amplifier. 40 is the input coupling capacitor to 39. 41 and 42 are tuned transformers tuned to two intermediate frequencies, 255 and 265 kc. The signals from the trans- The .rectified signal is smoothed in capacitors 47 and 48. The power supply is 49.

' An example of suitable operating values for the circuit parameters of FIG. 7 is as follows:

Transistor 39 2N35 Tank circuits:

41 kc 255 42 kc 265 Capacitor 40 ,uf 0.01 Diode rectifiers 43-46 lN34 Operation The embodiment shown in'FIG. 1 may be used as a measuring device in the following manner.

The direct current source I is held at a fixed value and a transducer such as a thermocouple is substituted for the direct current source I The transducer is so connected that its voltage response as seen by the transistor 4 is of opposite polarity from that of the current source I as seen by the transistor 3.

When the transducer responds to some measurable quantity, the resulting current output lowers the effective D.C. resistance of the transistor 4 by a proportional amount. At the same time, the effective D.C. resistance of the transistor 3 is lowered in proportion to the constant current value of the direct current source 1 which acts as a standard reference value for the rebalance bridge.

Thus, a ratio is effected between the resistance values of the transistors 3 and 4 respectively.

The resistance ratio of the two transistors must equal the ratio of the sections of the variably tapped resistor 5 in'order for the bridge to be balanced. If the ratios are not equal, a voltage of magnitude and polarity proportional to the difference between the two ratios appears across the terminals A and B of the output system 1 1.

The output system 11 responds to the unbalance voltage across its terminalsA anus, and acts to mechanically adjust the values of the sections of the variably tapped'resistor 5 until the voltage across terminals A and B is equal to zero or an equivalent null value. The final value of the resistance ratio and the known reference output of the current source I determines the value of the unknown quantity being measured.

The operation of FIG. 3 is the same as that of FIG. 1 with the transistor units of FIG. 2 properly substituted for the transistor units of FIG. 1.

In FIG. 4, the terminals A and B correspond to the terminals A and B respectively, of the output system 11 as shown in FIG. 1. An unbalance voltage across A and B depending upon its polarity, causes one of the transistors 14 or 15 to conduct and energize its associated relay 13 and 19, respectively. The DC. motor 20 is energized for proper directional rotation to adjust the variably tapped resistor 5 (FIG. 1) by a means not shown. The motor is stopped when the unbalance voltage across A and B is brought to a null.

The operation of FIG. 5 is similar to that of FIG. 4, the difference residing in the types of transistors used and the resulting circuitry required.

For operation as a remote control the circuits of FIGS. 1, 6 and 7 are interconnected as shown by the corresponding letters. A 20% audio modulated tone varying between 255 and 265 kc. is used as the input at 1 When the audio carrier is varied in frequency the ratio of the two inputs at I and I as detected by the rebalance circuit varies and the circuit rebalances controlling the output system 11. Other information may be transmitted by the audio tone. Brief interruptions of the carrier do not afiect operation and may be used to send pulses. The part of the circuit given in- FIG. 6 receives these pulses What is claimed is:

1. A self balancing bridge circuit including first and second direct current source inputs having a common terminal therebetween, said first source providing a standard value of direct current and said second source providing a variable value of direct current in response to a predetermined condition; first and second bridge arms, said first bridge arm comprising a first transistor of a predetermined polarity having the emitter terminal thereof connected to the base terminal thereof through said common terminal and said first source, and said second bridge arm comprising a second transistor of an opposite polarity from said first transistor having the emitter terminal thereof connected to the base terminal thereof through said common terminal and said second source, said transistors each having a collector terminal, said first and second bridge arms extending from said common terminal to the respective collector terminals through said emitter terminals whereby an impedance is provided in each bridge arm by the respective transistor therein having a magnitude proportional to the value of the respective direct current source inputs; third and fourth bridge arms comprising a single fixed resistor connected between said collector terminals of said first and second transistors and having a variable tap intermediate the ends thereof providing a variable common connection between said third and fourth bridge arms, whereby an impedance is provided in each of said third and fourth bridge anns having relative magnitudes dependent upon the position of said'variable tap; a power source connected across said collector terminals whereby said first and second bridge arms and said third and fourth bridge arms, respectively, form first and second voltage dividers having said common terminal and said variable tap, respectively, as the intermediate terminals thereof whereby a voltage difference appears between said terminals as a function of the difference in the impedance ratio of said first and second voltage dividers; and unbalance detecting means connected between said common terminal and said variable taprcsponsive to said-voltagediiference to automatically reposition said variable tap to a position wherein the impedance ratios of said first and second voltage dividers are equal, including means for providing an indication of the value of said ratio.

2. The device as described in claim 1 wherein said unbalance detector means comprises a pair of common emitter connected transistors of like polarity, a pair of relays connected one in the collector circuit of each transistor and having a common power supply, a pair of input terminals one to each base electrode of said transistors for receiving a voltage input from said common terminal and said variable tap, respectively, 'a pair of crystal, diodes associated one with each of said pair of transistors, and

connected from base to emitter thereof, whereby a voltage of improper polarity when applied to one of said transistors is bypassed by the diode associated therewith to allow the other of said pair of transistors to conduct and energize proper relay and a reversible motor in driving relationship with said variable tap and controlled by said pair of relays for adjusting said tap in a direction corresponding to the value of said voltage input.

3. The device as claimed in claim. 1 wherein said unbalance detector means comprises a dilferential relay controlled servo-mechanism for automatically adjusting said variable tap and thereby adjusting the impedance ratio of said single fixed resistor.

4. The device as described in claim 1 wherein said unbalance detector means comprises a pair of common emitter common base connected transistors of opposite polarity, a pair of relays connected one in thecollector circuit of each of said transistors, individual power supplies for each of said relays for biasing one of said relays positive and one negative with respect to the common emitter circuit of said pair of transistors, a pair of input terminals arranged one in the common base circuit and one in the common emitter circuit of said transistors for receiving a voltage input from said common terminal 5. In a rebalance bridge. device including a plurality of bridge arms comprising first and second variable ratio voltage dividers, said first voltage divider comprising variable irnpedance means responsive to individual input signals, and a plurality of input signals for said first voltage divider; a device for detecting failure of said input signals to said first voltage divider comprising, a power supply mutually connected across both of said voltage dividers at a pair of terminals common thereto, a dropping resistor connected between one of said terminals and the corresponding terminal on said power supply whereby the total current from both of said voltage dividers flows through said dropping resistor, a transistor con-' nected by its emitter between said dropping resistor and said one of said terminals and by its base to a source of reference potential, and a relay connected between the other of said terminals and the collector of said transistor, whereby upon failure of. any of said input signals to said first voltage divider, the input responsive variable impedance means therein cause a decrease in current flow through said first voltage divider reducing the total current flow in said dropping resistor, said decrease in current providing a resultant decrease in voltage drop across said resistor and a corresponding decrease in emitter voltage allowing said reference voltage at the base of said transistor to cause said transistor to conduct and energize said relay as an indication of input failure.

6. The device as described in claim 5 wherein said source of reference voltage comprises a voltage divider connected across the terminals of said power supply.

References Cited in the file of this patent UNITED STATES PATENTS 2,652,489 Robinson Sept. 15, 1953 2,654,841 Dutton Oct. 6, 1953 2,778,978 Drew Jan. 23, 1957 2,806,207 Edwards Sept. 10, 1957 2,823,351 Page Feb. 11, 1958 2,859,402 Schaeve Nov. 4, 1958 2,860,193 Lindsay Nov. 11, 1958 2,871,348 Hutchinson et al. Jan. 27, 1958 2,882,450 McCabe Apr. 14, 1959 FOREIGN PATENTS 162,171 Australia Jan. 21, 1954 

